Chitosan as tear substitute: A wetting agent endowed with antimicrobial efficacy

A cationic biopolymer, chitosan, is proposed for use in artificial tear for mulations. It is endowed with good wetting properties as well as an antibac terial effect that are desirable in cases of dry eye, which is often compli cated by secondary infections. Solutions containing 0.5% w/v of a Low molec ular weight (M-w) chitosan (160 kDa) were assessed for antibacterial effica cy against E. coli and S. aureus by using the usual broth-dilution techniqu e. The in vitro evaluation showed that concentrations of chitosan as low as 0.0375% still exert a bacteriostatic effect against E. coli. Minimal inhib itory concentration (MIC) values of chitosan were calculated to be as low a s 0.375 mg/ml for E. coli and 0.15 mg/ml for S. aureus. Gamma scintigraphic studies demonstrated that chitosan formulations remain on the precorneal s urface as long as commonly used commercial artificial tears (Protagent(R) c ollyrium and Protagent SE(R) unit-dose) having a 5-fold higher viscosity.